Blocking oscillators



Sept. 11, 1956 w 2,762,920

BLOCKING OSCILLATORS Filed Feb. 26, 1954 717 7HV/0QTRON GRID //v VENro/z THOMAS A. WE/L RNEY BLOCKING CILLATORS Thomas A. Wail, Wellesiey,Mass, assignor to Raytheon Manufacturing Company, Waitham, Mesa, :1corporation of Delaware Application February '26, 1954, Serial No.412,720

4 Ciaims. (Ci. 25tl36) This invention relates to means for generatingelectromagnetic energy and more particularly to an improved blockingoscillator adapted for supplying short-circuited loads.

Blocking oscillators of the prior art are characterized in that thefeedback from the plate circuit to the grid circuit is in parallel withthe load. Such oscillators operate satisfactorily if the load circuitimpedance is relatively high, that is, when the oscillator outputcircuit is coupled to an open circuit or to a circuit which draws arelatively small current. When such blocking oscillators are used tosupply a load which draws relatively large currents, seriousdifliculties are encountered. For example, when such oscillators areused as a driver for thyratron grids, the action of the blockingoscillator is interrupted by the short-circuit placed across the outputcoil of the blocking oscillator transformer when the thyratron fires. Asa result, an erratic series of short pulses is generated instead of asingle pulse of the resquired duration.

Although this problem may be partially solved in low power thyratrons byinserting a resistor in series with the thyratron grid, so that a directshort-circuit does not appear across the blocking oscillatortransformer, the larger thyratrons now in common use require such a lowimpedance driver that some other means of solution must be resorted to.

In accordance with this invention a feedback winding is placed in serieswith the load rather than in shunt with the load. The regenerationthereby obtained is proportional to the load current so that theregenerative feedback continues and actually improves when the load isshortcircuited. This current feedback is in contradistinction to thevoltage feedback of prior blocking oscillator circuits.

In order to adapt the blocking oscillator of the subject invention foroperation into an open-circuited load, a resistor is connected acrossthe output winding of the blocking oscillator so that sufficient currentfeedback is provided for satisfactory operation of the circuit.

An additional advantage obtained with this circuit is that the source ofthe triggering pulse is not loaded by any coupling to the load as inprior blocking oscillator circuits.

In the drawing a schematic diagram of a blocking oscillator inaccordance with the invention is shown.

Referring to the drawing, the blocking oscillator circuit includes avacuum tube or other electron discharge device having at least a cathode11, an anode 12, and a control electrode 14. Although the electrondischarge device is shown for the sake of clarity as a triode, it maycontain other control electrodes. For example, in one practicalembodiment of the invention, electron discharge device 10 is a beampower pentode amplifier. The principles of this invention, however, areequally applicable to a blocking oscillator using any type of amplifier.The cathode 11 of tube 10 is grounded at 15. Anode 12 is connectedthrough serially-connected windings 16 and 17 of transformers 20 and 22,respectively, to a terminal 19 of a suitable source of positive voltage.The relative position of windings 16 and 17 may be reversed; that is,one terminal of winding 17 may be connecteddirectly to anode 12 and theother terminal connected to the lower end of winding 16. In this case,the upper end of winding 16 is connected directly to terminal 19. Grid14 is connected through a second winding 23 of transformer 22 and.

through a capacitor 24 to ground 15. A resistor 25 serves the dualpurpose of a discharge circuit for capacitor 24 and a biasing circuitfor grid 14, and one end of said resistor is connected to the terminal26 of a source of biasing voltage.

When a positive input trigger pulse is applied to the winding 29 oftransformer 22, the voltage induced in the. grid winding 23 overcomesthe bias on grid 14 and causes the grid to become more positive withrespect to the cathode. This positive grid voltage causes anodecurrentto flow through winding 16 of transformer 20 as well as throughserially-connected Winding 17 of transformer 22; this current, in turn,induces a voltage in the grid winding 23 of transformer 22. The dotsadjacent to each winding indicate similar polarities. Because of thepolarity of the windings, the induced voltage in winding 23 causes grid14 to become more positive and more anode current flows in tube 10.Because of this regenerative action, the anode current rises veryrapidly. A rectifier 28 may be used to revent undesirable coupling tothe source of trigger. pulse after the regenerative action. has beeninitiated.

When the thyratron grid voltage becomes suificiently positive for thethyratron to fire, a virtual short circuit is connected across outputwinding 30 and the current in anode winding 16 increases suddenly. Thisincreased current, alsov flowing in winding 17, causes an increase incurrent in winding 23 and the grid 14 of tube 10 becomes still morepositive. In other words, tube 10 is driven heavily after the load isshorted out, in comparison with the conventional blocking oscillator inwhich a short circuit across the output winding results in a suddendecrease in grid voltage to the point. where regeneration ceases.

Grid 14, when driven positive relative to cathode 11, draws current andthe grid current flowing through capacitor 24 to ground causes anegative charge to accumulate on the plate of the capacitor 24 nearestthe grid. The polarity of the. plates of grid capacitor 24 during thistime is as shown in the drawing. The voltage across capacitor 24gradually rises until eventually it becomes sufiicient to overcome thevoltage across the grid winding 23; the regenerative process thenreverses, the tube ceases, to draw current, and the output voltage dropsto zero. The period of the output voltage waveformis thus determined inpart by the value of capacitor 24. After the grid potential drops belowcutoff, the charge on capacitor 24 leaks ofi through resistor 25 untilthe capacitor is once more in a discharged condition awaiting arrival ofthe next trigger pulse. Other means for terminating the output voltagemay also be used. For example, reliance may be had upon saturation ofthe core of transformer 22 in the manner well known in the blockingoscillator art. Alternatively, a delay line may be included in the gridcircuit of the blocking oscillator to accomplish the same results.

Unlike the conventional blocking oscillators, which are particularlysuited for operation into an open circuit, means must be provided in theblocking oscillator circuit of the invention to permit operation into anopen circuit. In order to provide suflicient load for regeneration inthe case of an open-circuited load, a resistor 32 is connected in shuntwith transformer winding 30. In this way, there will always be some loadin the circuit.

Inspection of the circuit will show that when the tube 10 is in thecut-off condition, there are no loads on any of Patented Sept. .11,1956v the windings on the transformer 22, so that negligible drivingpower is required to trigger the tube into conduction, after which thetube supplies its own driving power. Other methods of inserting thetrigger pulse into the grid circuit may, of course, be used, and winding29 may then be omitted. For example, the trigger pulse may beapplieddirectly to the grid 14 by way of an appropriate coupling capacitor.Alternatively, the circuit may be made free running, i. e., may be madeto deliver an output pulse at regular intervals, without trigger, byadjustment of the bias voltage supplied to the terminal 26 to a valuewhich will not maintain the tube in a cut-off condition; in this case atrigger pulse is not necessary, but may be used for synchronization ifdesired.

This invention is not limited to the particular details of construction,materials and processes described, as many equivalents will suggestthemselves to those skilled in the art. It is accordingly desired thatthe appended claims be given a broad interpretation commensurate withthe scope of the invention within the art.

What is claimed is:

1. A blocking oscillator for providing an output waveform when triggeredby an input trigger pulse comprising an'electron discharge device havingat least an anode, a cathode, and a control grid, a first transformerhaving a primary winding and a secondary winding, said primary windingconnected in series with said anode, a load circuit coupled to saidsecondary winding, said load circuit including a resistor connected inparallel with said secondary winding, a second transformer having afirst winding in series with said primary winding and a second windingin series with the grid of said electron discharge device, meansinductively coupled to said second winding for introducing a triggerpulse into the grid circuit of said electron discharge device, and meansincluding said second transformer for effecting regenerative currentfeedback in said electron discharge device which is proportional to thecurrent in said load circuit.

2. A blocking oscillator for providing an output waveform when triggeredby an input trigger pulse comprising an electron discharge device havingat least an anode, a cathode, and a control grid, a source of anodepotential, a first transformer having a primary winding and a secondarywinding, a second transformer having a first winding and a secondwinding, said primary winding and said first Winding serially connectedbetween said anode and Said source, a load circuit coupled to saidsecondary winding, said second winding connected in series with saidcontrol grid, means inductively coupled to said second winding forintroducing a trigger pulse into the grid circuit of said electrondischarge device, a shunt combination of a resistor and a capacitorconnected in. series with the grid of said electron discharge device,said capacitor being charged by conduction of said electron dischargedevice to eventually terminate said output waveform and discharged bysaid resistor during the intervals between successive trigger pulses,and means including said second transformer for efiecting regenerativecurrent feedback in said electron discharge device which is proportionalto the current in said load circuit.

3. In combination, an electron discharge device having at least ananode, a cathode, and a control grid, a source of anode potential, afirst transformer having a primary winding and a secondary winding, asecond transformer having a first winding and a second winding, saidelectron discharge device having an output circuit including said firstwinding and said primary winding serially connected between said anodeand said source, a load circuit coupled to said secondary winding, saidelectron discharge device having an input circuit including a capacitor,a resistor and said second winding, said resistor providing a dischargepath for said capacitor during a portion of the operating cycle of saidelectron discharge device, means responsive to a predetermined degree ofdischarge of said capacitor for intiating the flow of current in saidoutput circuit and said load circuit, means responsive to the flow ofcurrent in said load circuit for effecting regenerative current feedbackin said electron discharge device and for charging said capacitor, meansresponsive to a predetermined degree of charge of said capacitor forterminating the flow of current in said output circuit and said loadcircuit.

4. In combination, an electron discharge device having at least ananode, a cathode, and a control grid, 9. source of anode potential, afirst transformer having a primary winding and a secondary winding, asecond transformer having a first winding and a second winding, saidelectron discharge device having an output circuit including said firstWinding and said primary winding serially connected between'said anodeand said source, a load circuit coupled to said secondary winding, saidelectron discharge device having an input circuit including a capacitor,a resistor and said second winding, said resistor providing a dischargepath for said capacitor during a portion of the operating cycle of saidelectron discharge device, means responsive to a trigger pulse forinitiating the flow of current in said output circuit and said loadcircuit, means responsive to the flow of current in said load circuitfor eflt'ecting regenerative current feedback in said electron dischargedevice, means including said capacitor for terminating the flow ofcurrent in said output circuit and said load circuit prior to thearrival of the next trigger pulse.

References Cited in the file of this patent UNITED STATES PATENTS1,733,614 Marrison Oct. 29, 1929 FOREIGN PATENTS 145,255 Australia Feb.19, 1952

